1. Field of the Invention
The invention relates to a drive system for dental handpieces of the type which have a rotor secured to a motor shaft where the rotor is mounted by means of at least one anti-friction bearing having an outer race and an inner race and a plurality of rolling elements arranged between the races.
2. Description of the Related Art
Medical or dental handpieces generally comprise an instrument portion for receiving a dental tool, for example a turbo-drill, a drive motor for driving the rotating dental tool, and a hose portion that has a media-supply hose for supplying specific supply media for the operation of the dental tool, such as, for example, current, spray or cooling air, spray water, etc.
FIG. 7 shows, by way of example, the three individual components: the instrument portion 1 with the dental tool 5 rotatably mounted on the head portion 6, the drive motor 3 and the hose portion 2 with the media-supply hose 4, which components are coupled by being attached directly one after the other. Such a structure is known, for example, from DE-C2 28 34 099. An alternative kind of structure is shown in FIG. 8. The drive motor 3 here is a so-called motor cartridge which is held in a hollow space formed by the instrument portion 1 and the hose portion 2.
An electric motor, in particular a d.c. motor, as known from DE-A1 196 04 628 belonging to the applicant, is, for example, used as the drive motor. The drive motor substantially comprises a rotor magnet, which is rotatably mounted by way of a motor shaft, and a stator having a self-supporting stator air-gap winding which has free spaces for media lines that supply specific supply media to the dental instrument that can be coupled thereto. The motor shaft is mounted in a motor housing by means of a front and a rear motor bearing.
Usually, anti-friction bearing systems are used as the motor bearings, said anti-friction bearing systems being composed of an inner bearing race, an outer bearing race and a plurality of rolling elements that are arranged between the two bearing races, with both the bearing races and the rolling elements being formed of steel in a manner known per se. As an alternative to the d.c. motor that is described, it is also possible to use an a.c. motor.
In addition to an electric motor (d.c. motor or a.c. motor) it is also possible to use an air motor as the drive motor. Such a motor is, for example, disclosed in DE-C2 32 15 255 belonging to the applicant. As follows in particular from FIGS. 5 and 7 of this printed specification, the air motor that is formed as a a lamellar motor has a central shaft that is rotatably mounted in a circular chamber, which is offset in relation to the center, and has radial slots, in which lamellae are pressed radially outwards as a result of the action of the force of a spring so as to rest against the inner wall of the chamber. The shaft of the air motor is also mounted in the housing by means of anti-friction bearing systems.
Other known air motors have a rotor in the form of a turbine wheel against which a compressed-air flow can flow tangentially or along a secant.
Since, in contrast with the above electric motor, the air motor is basically suited to withstand repeated sterilization, the air motor can also be a fixed component part of the instrument portion. When an electric motor is used, on the other hand, the latter must be detachably connected to the instrument portion in order to separate it from the instrument portion for the sterilization process, since the electronic components of the electric motor do not generally withstand repeated sterilization at least on a permanent basis.
Furthermore, various safety regulations are to be followed in the case of dental handpieces. Thus for, example, DIN EN ISO 7494, December 1997, xe2x80x9cZahnxc3xa4rztliche Behandlungsgerxc3xa4texe2x80x9d exists, laying down requirements and testing methods for dental treatment units irrespective of their design. Collected together under item 5.3 of this DIN-regulation inter alia there are electrical requirements, the observance of which is to guarantee that injuries to the patient and/or the personnel carrying out the treatment, for example as a result of an electric shock, are avoided.
Since the live components of dental handpieces extend into the drive motor, and the transmission elements of the handpieces including dental tools are mainly made of metal and thus are electro-conductive, expensive protective measures must be taken in the dental handpieces.
It is therefore an object of the present invention to provide a drive system of the kind mentioned by way of introduction in which further precautions for the observance of the electrical safety requirements are taken in a simple manner in order to increase further the safety of the patient and of the personnel carrying out the treatment.
This object is achieved by means an anti-friction system having rolling elements which consist of a non-electroconductive material. The use of steel anti-friction bearing systems with rolling elements that consist or are formed of non-electroconductive material guarantees electrical insulation between the stator or motor housing and rotor of the drive motor. As a result, current is prevented from being able to flow off by way of the ball bearings and the housing of the drive motor to the patient or to the personnel carrying out the treatment in the event of a defect of the drive motor.
Steel anti-friction bearing systems that have ceramic rolling elements (so-called hybrid anti-friction bearings) or fully ceramic anti-friction bearing systems are advantageously used to mount the motor shaft of the drive system. On account of the special material properties that ceramic materials have, this results in further advantages. The use of silicon nitride (Si3N4) for the rolling elements and possibly the bearing races is particularly advantageous here.
In this connection, in addition to the great electrical resistance in particular the lower specific gravity, the lower thermal conductivity, the clearly better resistance to chemicals and disinfectants and/or sterilizing agents, and the better temperature stability than steel are to be mentioned as advantageous material properties of ceramic materials.
Further configurations and developments of the present invention are disclosed and claimed herein.